All the protein components required for the formation of an initiation complex utilizing artificial templates (AUG triplet or Poly (U)) have been purified to homogeneity (IF-MI, IF-MP IF-M2A, IF-M2Balpha, IF-M2Bbeta, EF-1, EF-2). There appear to be two distinct pathways for initiation complex formation, one utilizing IF-MP to direct the binding of initiator tRNA, the other using IF-M1. Despite differences between the requirements for IF-MP or IF-M1 dependent binding of initiator tRNA to 40S subunits, the subsequent requirements for GTP, AUG, IF-M2A, IF-M2Balpha, IF-M2Bbeta, and 60S subunits to achieve an 80S initiation complex are identical. More recent experiments have indicated that three additional initiation factors (M3, M4, M5) are required for the translation of globin mRNA. At this point it is not clear how each of the factors functions. There is evidence to suggest that IF-M3 directly binds mRNA, specifically at the 5' end of the mRNA molecule. Neither IF-M4 nor IF-M5 appears capable of binding globin mRNA. Whether these latter factors function in the assembly or regulation of an 80S initiation complex containing globin mRNA is currently under investigation.